DOI： 10.1299/transjsme.17-00380]

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DOI： 10.3811/jjmf.30.467

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Publishing type：Research paper (international conference proceedings)  

© 2015 The Authors. The void fraction profile in a boiling channel is essential in analyzing convective flow boiling, where several investigations have been conducted. But due to the difficulty in the treatment of the non-thermodynamic equilibrium phenomena under subcooled conditions, the issues in comprehensive void fraction profile has not been solved, yet. To improve the understanding of these phenomena, detailed measurement results are required. In this investigation, by using five kinds of test sections, i.e. I.D.=3 mm L=400 mm, I.D.=5 mm L=200, 400, 1000 mm, and I.D.=10 mm L=400 mm, the void fraction was measured quantitatively over the whole length. For the measurements, thermal neutron radiography at the B-4 port of the Kyoto University Research Reactor was used. This facility is designed for the visualization of forced convective flow boiling in vertical tubes. To introduce the performance of this facility, this paper presents the measurement results of void fraction and the estimation results briefly.

DOI： 10.1016/j.phpro.2015.07.085

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DOI： 10.1016/j.phpro.2015.07.085

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Begell House Inc.  

Critical heat flux (CHF) is one of the key design factors for boiling heat transfer equipment. Thus, CHF, especially under upward flow condition, has been widely investigated, but the characteristics of CHF for downward flow are quite different from for upward flow. In downward flow, the complex flow structure is formed due to the counter force between the buoyancy and inertia. In view of thermal-hydraulic characteristics, downward flow should be avoided in boiling equipment. However, in a research reactor, downward flow is applied as a simplified cooling method of the reactor core. The objective of this investigation is to grasp the influence of the tube diameter on CHF in downward flow, because CHF in downward flow is closely related to the flow structure, which is influenced by the diameter and the flow velocity. The CHF experiment was carried out with a forced convective boiling system by using various inner diameter tubes in upward and downward flows. On the basis of the obtained pressure drop of the test section, behavior of inlet fluid temperature, and the location of CHF, the experimental CHF could be classified into four modes, i.e., complete dryout of falling liquid film, CHF due to flooding, CHF caused by hydraulic instability, and liquid film dryout in annular flow. These CHF are discussed by using the CHF model based on the regime-based modelling.

DOI： 10.1615/MultScienTechn.v27.i1.50

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Language：Japanese   Publisher：Japan Society of Refrigerating and Air Conditioning Engineers  

The frost layer with melting water was measured by using a neutron radiography in the defrosting process on the aluminum finned-tube heat exchanger under the forced-convection. The water deposition distributions were estimated quantitatively in every 5 seconds for 10 minutes of the defrosting period. The melting water behavior was investigated by comparing the water deposition distribution before defrosting. The initial stage of the defrosting was referred to as the melting progressing period, in which the melting water penetrated into the water permeation layer in the frost thickness direction. The melting water penetration into the spanwise direction of the fins was not observed by the neutron radiography. After 180sec from starting the defrosting process, the frost at the fin front edge and the surrounding the tubes were melted, then, the water permeation layer was saturated by the melting water. The neutron radiography images indicated the melting water penetration into the spanwise direction of the fins. The total migration volume of the melting water into the spanwise direction was about 30% of the total frost deposition.

DOI： 10.11322/tjsrae.15-29_OA

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Dryout of counter-current two-phase flow is one of key issues in chemical and/or industrial systems. The aim of the present study is to provide insights into the dryout phenomena of such counter-current two-phase flow of binary gas and liquid in a vertical tube. Experimental results suggest a significant influence of the subcooling of water and the binary gas flow rate on the dryout characteristics. The observed dryout was classified into three modes, i.e.,film breakdown, dryout due to flooding and dryout due to critical flooding. At the low inlet air flow rate, dryout characteristics wereaffected by subcooling of water. The test section was partially overheated owing to the liquid film breakdown due to the Marangoni effect. At the moderate inlet air flow rate, the dryout is induced by the reduction on the falling liquid film due to flooding. At the high gas flow rate, most of the water was carried over due to the critical flooding. In the latter two cases, there was no influence of subcooling of water on dryout. These dryout phenomena were successfully realized in the numerical simulation based on the one-dimensional heat and mass transfer model, i.e., energy balance of a heat input, a heat release rate from the heating surface and a mass transfer rate due to phase change. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijmultiphaseflow.2014.09.002

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Language：Japanese  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS INC  

Critical heat flux (CHF) is an important design factor for boiling two-phase flow equipment, such as boilers and others. In actual boiling systems, the water tube suffers from the nonuniform heating and/or tube inclinations. The objective of this investigation is to understand the influence of tube inclination on CHF characteristics under such high-heat-flux conditions. The experimental investigation was conducted with a forced convective boiling system by using a uniformly heated tube and a nonuniformly heated tube set at arbitrary inclination angles phi. The obtained CHF was strongly influenced by the circumferential location of local maximum heat flux point and tube inclination. In the case of the normal tube, the CHF always occurred by the liquid film dryout at the top of the tube. In the case of the nonuniformly heated tube, the influence of the inclination on the CHF characteristics strongly depended on the circumferential heat flux distribution. When the the heat flux at the bottom was higher than that at the top, two types of CHF mechanism, namely, low-quality CHF upstream of the test section under high-mass-flux condition, and liquid film dryout at the tube exit under low-mass-flux condition, were observed. When the heat flux at the top was higher than that at the bottom, intermittent dryout was observed as the dryout mechanism. These CHF characteristics could be categorized by using the CHF ratio against the value of the vertical upward flow with the modified Froude number, which corresponded to the influence factor of disturbance wave.

DOI： 10.1080/01457632.2013.832581

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Language：Japanese   Publisher：Japan Society of Refrigerating and Air Conditioning Engineers  

Frost formation on heat exchangers can have a serious impact on their heat transfer performance due to the thermal resistance and pressure drop by the frost layer. Many studies had been carried out to investigate frosting on a flat plate, cylindrical surface and heat exchangers. In conventional methods of measuring the frost formation, the frost is scraped from the surface, making the temporal and spatial distributions of its frost deposition difficult to determine. In the present study, the frost formation on a cold flat plate is investigated by using neutron radiography. Neutrons are strongly attenuated by the water molecules in the frost layer, but not by the aluminum cold flat plate. The frost formation can be quantitatively estimated based on neutron beam attenuation. The mass attenuation coefficient of water to the neutron beam is estimated by the calibration test using the phantom piece. Frost formation and growth on the cold flat plate could be clearly measured by neutron radiography. The frost deposition was measured every 10 min, so that the local frost accumulation rate could be estimated from differential images. The spatial and temporal distributions of the local mass transfer coefficient could be successfully measured using neutron radiography.

DOI： 10.11322/tjsrae.31.207

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Language：Japanese   Publisher：THE JAPANESE SOCIETY FOR MULTIPHASE FLOW  

In this study, the rising velocity of Taylor bubbles in inclined tube was investigated. In the experiment, the air-water two-phase flow system equipped with the Taylor bubble injector, which can inject arbitrary size Taylor bubble with a certain distance, was used. The inclined angle was 30-90 degree, the tube inner diameter was 20mm, the dimensionless bubble diameter λ was 0.6-2.0 and liquid velocity was 0.011-0.053m/s. As the result, the influence of the tube inclination and bubble size on the correlation for the bubble velocity with the separation distance of two consecutive bubbles was presented. On the basis of these results, the characteristics of the Taylor bubble movements were explained. Moreover, the fundamental data of two consecutive bubbles, i.e. the maximum trailing bubble velocity, the location of maximum velocity, the effective range of velocity and the damping ratio of velocity were reported.

DOI： 10.3811/jjmf.27.306

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Other Link： https://jlc.jst.go.jp/DN/JALC/10024372359?from=CiNii

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier B.V.  

Although the flow oscillation strongly affects the characteristic of the critical heat flux, the detailed feature of these phenomena had not been fully understood, so far. One of the reasons of the lack of the reports is owing to the characteristics of the flow oscillation, i.e. the flow oscillation is strongly influenced by the operating condition. This means the oscillatory condition changes by the heating condition, thus general discussion becomes difficult. In this series of investigations, the critical heat flux (CHF) was investigated under artificial flow oscillation generated by a mechanical flow oscillator. By using these means, the influence of the flow oscillation was systematically obtained, and several results and model were presented. In this investigation, the similar experimental investigation was conducted to estimate the dynamic movement of the void fraction. In the visualization procedure, 0.03 second exposure image which synchronized with the flow oscillator was taken, and by using the ensemble averaging of 34 images, the image which had enough dynamic range could be reconstructed. © 2013 The Authors. Published.

DOI： 10.1016/j.phpro.2013.03.031

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Language：Japanese   Publisher：THE JAPANESE SOCIETY FOR MULTIPHASE FLOW  

Immiscible two components flow is widely observed in several engineering equipments such as pipeline, μ-TAS and so on, and it has been also utilized as the simulation of the two-phase flow under high pressure conditions. However, the knowledge of fluid characteristics in mini-channel is still not enough, especially the influence of the methods of the mixing is not clear. In order to clarify the flow characteristic of oil-water mixture in horizontal mini-channels, the experimental investigation was conducted by using a forced convective flow system with two different mixers with two mixing manners. The test section was made of glass tube with 0.53mm and 2.09 mm in inner diameter. As the experimental results, the several flow patterns were identified and flow pattern transition was correlated by using Weber number of each phase. The pressure drop for 2.09 mm took the characteristics of ordinary tube, while 0.53 mm took the typical characteristics of capillary tube. The obtained pressure drop showed a good agreement with Lockhart-Martinelli correlation.

DOI： 10.3811/jjmf.26.302

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Other Link： https://jlc.jst.go.jp/DN/JALC/10009862219?from=CiNii

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

The spacer of Boiling Water Reactor (BWR) becomes the flow obstacle. Moreover the clearance between fuel rods of the innovative Water Reactor for Flexible fuel cycle (FLWR) becomes very narrow. Thus understanding of the thermal-fluid characteristics in the boiling channel equipped with the flow obstacle becomes more important. In this study, to clarify the flow obstacle effect, the experimental investigation was conducted with the forced convective boiling system. The test section was 8 mm in inner diameter, and the rod-type flow obstacle, which had 3.6 mm in diameter and 20 mm in length, was installed. The blockage ratio beta = 20.3 % which was the similar value of the present BWR reactor. The heating length L-T was taken three different lengths, L-T = 810, 840 and 900 mm As the experimental results, the CHF was increased by the installing of the flow obstacle, and it was strongly influenced by the axial position of the flow obstacle. In the most of the case, the liquid film dryout was detected at the exit of the test section, while the CHF was observed at the upstream of the flow obstacle in the case of the L-T = 810 mm. The calculation results of the liquid film flow model have shown a good agreement with these experimental results by using the presented influence length of the flow obstacle.

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Critical Heat Flux (CHF) in a non-uniformly heated tube is a very important design factor of actual boiling equipment. In this series of studies, the CHF in a non-uniformly heated tube has been evaluated by considering the re-distribution of a liquid film caused by the wave interaction. In the present investigation, in order to estimate the influence of the magnitude of the heat flux, the CHF experiment was conducted. The experimental apparatus was the same as the forced convective boiling system presented in the previous paper, i.e. the eccentric tube with 20 mm I.D., 24 mm O.D., but heated length was just only 450 mm to keep the high heat flux condition. The experimental result indicated the influence of the magnitude of the heat flux as the entrainment increased. In this investigation, two kinds of the CHF mechanisms were observed, i.e. liquid film dryout at the high quality condition and departure from nucleate boiling (DNB) at the low quality condition, respectively. This obtained CHF has been evaluated by using the film flow model, and the empirical correlation of the spreading coefficient of liquid film re-distribution was proposed.

DOI： 10.1002/htj.20333

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Language：English   Publishing type：Research paper (scientific journal)  

This paper describes the flow patterns of carbon dioxide two-phase flow at high pressure observed in horizontal minichannels ranging from 0.51 to 3.0 mm in diameter, together with the flow pattern maps and related boiling heat-transfer characteristics. The observed flow patterns are mainly classified into bubbly, slug, slug-annular, and annular flows, similar to conventional pipes, while phase stratification tendency is still significant even in a 1.0 mm tube, so that heat transfer at high pressure shows significant differences in the upper and lower walls, especially in 2.0 and 3.0 mm tubes. Such phase stratification with reference to heat transfer is roughly scaled by means of boiling number and Bond number. The newly developed simulation model by the authors for conventional-sized tubes is successfully applied to 2.0 and 3.0 mm pipes, but not to 0.51 and 1.0 mm tubes. This model suggests that thermal flow behavior at higher Bond number Bo than 8.2 is similar to that of conventional-sized tube, and cases less than Bo = 8.2 show minichannel behavior. The heat transfer in these minichannels is well-predicted with Schrock-Grossman type correlation with nucleate and forced-convective effects, while in larger tubes, e.g., 2.0 and 3.0 mm, the heat transfer is mainly dominated by nucleate boiling in the present experimental ranges. © 2010 by Begell House, Inc.

DOI： 10.1615/MultScienTechn.v22.i2.20

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Increasing attention has been focused on carbon dioxide (CO2) heat Pump system where the temperature level is rather low, while the operating pressure is rather high. in this system, the density difference between vapor and liquid becomes rather small, which significantly affects flow patterns. Low tension and latent heat also have significant influence on two-phase flow patterns and heat transfer. This paper describes experimental and numerical investigation on flow patterns and heat transfer characteristics of boiling flow CO2 at high pressure in horizontal small-bore tubes ranging from 1.0 mm to 3.0 mm I.D. Even though the density difference is rather small at high pressure, phase stratification takes place, which leads to the intermittent dryout at the upper wall. So far developed discrete bubble model by the authors for vertical flows is modified so as to include horizontal flow mechanisms. The predicted flow patterns with this new model agree on the whole with the experimental observation. (C) 2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijmultiphaseflow.2009.04.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

In the framework of pattern dynamics approach, the discrete bubble model was developed for simulating inherent fluctuation of void fraction in a horizontal two-phase flow. Then flow patterns were identified based on the statistical properties of void fraction fluctuation, and the flow pattern map agreed with the experimental observation of high-pressure two-phase flow Of CO(2) in horizontal tubes. The time-averaged pressure drop and the void fraction obtained in the simulation agreed reasonably with the existing correlations. Thus the horizontal flow version of the discrete bubble model demonstrates its relevance in simulating inherent fluctuation of two-phase flow. (C) 2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijheatmasstransfer.2009.08.018

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Principal heat transfer mechanisms in a fluidized bed have been classified into three categories, i.e. solid convection, gas convection and radiation. Among these mechanisms, the solid convection is a dominant mechanism in the bubbling fluidized bed. This solid convection is substantially caused by the bubble movement, thus the visualization of the void fraction distribution becomes a very useful method to understand the characteristics of the fluidized-bed heat exchanger. In this study, the heat transfer coefficient and the void fraction around the heat transfer tube with annuler fin were measured. For the quantitative measurement of the void fraction, neutron radiography and image processing technique were employed. Owing to the existence of the annuler fin, the restriction of the particle movements was put. This restriction suppressed the disturbance caused by tubes, and the influence of the tube arrangement on the flow and heat transfer characteristics could be clearly expressed. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nima.2009.01.151

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：DESTECH PUBLICATIONS, INC  

Fluidized-bed has high heat transfer performance, and then this technology is used in fluidized-bed boilers, such as PFBC (Pressurized Fluidized-bed Combustors), CFBC (Circulating Fluidized-bed Combustor) boilers. In these boilers, distributors are equipped at the bottom, and fluidized-gas is injected into the fluidized-bed through these distributors. Thus the arrangement and structure of the distributor strongly depend on the movement of fluidized-bed material and also depend on the performance of the fluidized-bed boiler. Thus, the design of the distributors is a very important factor in the design of fluidized-bed boilers. But, these designs are normally decided by empirical methods, and the detail is decided by trial and error. In this investigation the void distribution around the cap type distributor, which is widely used in commercial fluidized-bed boilers, was visualized by using thermal neutron radiography. In the experiment a cap type distributor was set at the bottom of the 150mmX140mmX578mm fluidized-bed, and the CT-processing was also applied to obtain the three dimensional void distribution around the distributor. As it resulted, three-dimensional void propagation after the injecting from the tuyere holes could be clearly visualized. The results are compared by using the two-dimensional experimental apparatus, and the effect of the three dimensional structure is discussed.

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Language：Japanese   Publisher：The Heat Transfer Society of Japan  

Kansai University Research Grants 2005-2006

DOI： 10.11368/tse.15.197

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Other Link： http://hdl.handle.net/10112/5954

Language：English   Publishing type：Research paper (scientific journal)  

Gas-liquid two-phase flow is a typical complex system with intrinsic spatiotemporal fluctuation in phase distribution, pressure drop, heat transfer, and so on, being an important subject left behind after extensive research on two-phase flow dynamics. Previously developed modeling is not appropriate in application to CHF problems at low quality and/or in downward flow. This is mainly because conventional modeling, including two-fluid modeling, is based on the continuous flow hypothesis. The proposed model, represented by the discrete bubble model, consists of a void propagation equation as a global rule and only a limited number of mechanical and geometrical relationships as local rules, i.e., a wake effect, gas compressibility, and a phase redistribution mechanism. Neglecting detailed mechanisms of two-phase flow, the spatiotemporal fluctuations in void fraction and pressure drop are numerically realized within the framework of the pattern dynamics approach.

DOI： 10.1615/MultScienTechn.v19.i4.30

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

CT-processing is very effective in obtaining 3-dimensional information for industrial instruments, and several trials have also been applied to fluidized-beds. In the CT-processing of fluidized-beds, X-rays are used mainly because they are readily availability. Similar processing can be performed by neutron-rays which penetrate most metals, but not some chemical substances, such as hydrogen, boron, gadolinium, which are opaque to the neutrons. Due to these unique characteristics, neutron radiography can be considered as a suitable visualization method of actual industrial instruments made of metal. Thus, neutron radiography also has significant advantages for the visualization of fluidized-beds. However, neutron radiography requires a nuclear reactor or an accelerator as the neutron source in order to obtain high quality images, which means that the real time CT-processing of multiphase flows by neutron radiography is quite difficult. Consequently, CT-images in this investigation were reconstructed by using time-averaged visualization images. Although time averaging makes the understanding of the void movement difficult, 3-dimensional characteristics of the void fraction propagation in fluidized-beds could be clearly visualized by using test sections with significant non-uniformity of the fluidized-gas distribution.

DOI： 10.1002/ppsc.200601066

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Language：English   Publishing type：Research paper (scientific journal)  

Recently, regional flow instability in two-phase flow system, i.e. flow fluctuations occurred only in the core region of nuclear reactor or multi-channel region without fluctuation of the total inlet flow, is attracting much interest. This flow instability is a significant problem for the systems from the viewpoint of safety and economy. Many investigations on the flow instabilities have been conducted so far, and respective stability criteria have been proposed, while these investigations focused normally on the one-channel system without flow maldistribution, and the resulting stability criteria are hardly applied to the regional flow instability problems. Thus in the present investigation, we conducted analytical investigation focusing not only on the whole system flow instability but also on the regional flow instability. The stability analysis was performed with lumped-parameter model of parallel boiling channels. Finally the stability criteria for the two types of the flow instabilities and the stability maps were obtained.

DOI： 10.1615/MultScienTechn.v18.i4.10

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Language：English   Publishing type：Research paper (scientific journal)  

In an actual boiling channel, the circumferential heat flux is not uniform. Thus, the understanding of the heat transfer characteristics of non-uniformly heated tube becomes an important design factor for conventional boilers, especially for the compact water-tube boiler with tube-nested combustor. The small compact boiler is operated at low-pressure and low-mass flux condition compared with the large scale boiler, so that the non-uniformity in heat flux may strongly affect the heat transfer characteristics. In this investigation, non-uniform heat flux distribution along the circumferential direction was generated by using Joule heating of SUS304 eccentric tubes. The heated length of test-section was 900mm, inner diameter was 20mm, and outer diameter was 24mm. The eccentricity of the tube was s 0, 0.5, 1.0 and 1.5mm. Corresponding maximum/minimum heat fluxes rations were 1.0, 1.7, 3.0 and 7.0, respectively. Experiments were conducted for upward and downward flows, with system pressures 0.3 and 0.4MPa, mass flux range 10-100kg/m2s and inlet temperatures 30 and 80deg.C. The eccentricity resulted in an increase in the CHF of the upward flow, while the effect was hardly observed in the downward flow. The effect of eccentricity on the CHF was well interpreted by the liquid film redistribution. In this paper, the local heat transfer coefficient along the circumferential direction was also presented.

DOI： 10.1615/MultScienTechn.v18.i4.40

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Heat transfer characteristics of a fluidized-bed heat exchanger are dominated by the characteristics of bed-material movement, especially, in the neighboring region of the heat transfer tube. In the present experiment, a simulated fluidized-bed heat exchanger model was partitioned into two channels to form an upward and downward flow simultaneously in the same fluidized-bed model. Then the total amount of circulating material was kept at the same value even at the different void fractions between two channels. The flow pattern of bed material was visualized by neutron radiography with introducing tracers into the fluidized bed. The simulated fluidized bed consisted of aluminum plates, and the bed materials were sands of 96% SiO2 (mean particle diameter: 0.154-0.321 mm, density: 2550 kg/m(3)). Bed materials were almost transparent for neutrons. On the contrary, tracer particles of about I mm diameter made of B4C with clay were opaque. Thus, the tracer particles were detected clear enough for PTV (Particle Tracking Velocimetry). The fluidized-bed behavior was then discussed in relation to the heat transfer characteristics around the heated tubes submerged in the bed. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nima.2005.01.094

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Owing to a wide variety in fluidization properties of particles, segregation phenomena are hardly avoided in industrial fluidized-bed facilities. For the stability and controllability in the operation of such fluidized-beds, understanding of the relevant mechanism of particulate segregation is indispensable. Many factors, such as the difference in particle size, density, shape, and also arrangement of distributors, can be pointed out as the dominant causes for the segregation. Thus, any marking of particles for quantitative measurement may severely influence the segregation characteristic to be measured. But neutron radiography can be used for the quantitative measurement without disturbing the segregation characteristic. For estimating the segregation phenomena, evaluations of the particle fraction and the void fraction are required. For this purpose, two types of radiographies, i.e., X-ray and neutron radiographies were used in this investigation. Experimental results demonstrated the high performance of this method in investigating of segregation phenomena. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nima.2005.01.103

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

In an actual boiling channel, e.g. boililer water-tubes, the circumferential heat flux is not uniform. Thus, critical heat flux (CHF) of non-uniformly heated tube becomes an important design factor of conventional boilers, especially for the compact water-tube boiler with tube-nested combustor. The small compact boiler is operated at low-pressure and low-mass flux condition compared with the large scale boiler, thus the redistribution of liquid film will strongly affect on the characteristics of CHF. In this investigation, non uniformly heat flux distribution along the circumferential direction was generated by using the Joule heating of SUS304 tubes which had the wall thickness distribution. The heated length of test-section was 900 mm, inner diameter was 20 mm and outer diameter was 24 mm. The center of the inner tube surface was shifted by ε = 0, 0.5, 1.0, 1.5 mm from the center of the outer tube surface. The heat flux ratio between maximum and minimum heat fluxes of these tubes correspond to 1.0, 1.7, 3.0 and 7.0, respectively. Experimental conditions were as follows
system pressures were 0.3 and 0.4 MPa, mass flux range were 10-100 kg/m2s, inlet temperatures were 30 and 80 deg. C. The experimental results showed an increase in the critical heat flux by the existence of the redistribution of the flow. These characteristics have been well explained by using the similar concept of Butterworth's spreading model.

DOI： 10.1299/kikaib.71.939

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Owing to a wide variety in fluidization properties of particles, segregation phenomena are hardly avoided in industrial fluidized-bed facilities. For the stability and controllability in operation of such fluidized-beds, understanding of the relevant mechanism of particulate segregation is indispensable. This paper describes an experimental observation of the particulate segregation in a binary mixture system visualized successfully by using a neutron radiography (NR). The NR gives real-time information of the segregation process, and this information will be very useful in understanding the segregation mechanism.

DOI： 10.1109/TNS.2005.844016

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Quantitative flow visualization of a gas-solid fluidized-bed installed vertical tube-bank has been successfully conducted using neutron radiography and image processing technique. The quantitative data of void fraction distribution as well as the fluctuation data are presented. The time-averaged void fraction is well correlated by the drift-flux model. The bubbles formed in the bed, rise along the vertical tubes and the observed bubble size is smaller than that in a free bubbling bed without tube-banks. The bubble diameter is well correlated by the modified Mori and Wen's correlation taking into account the pitch of tube arrangement. The bubble rise velocity is also well correlated by applying the drift-flux model. These results are consistent for both bed materials of Geldart's B- and A-particles, while the bubble size is significantly different between two kinds of particles. (C) 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.apradiso.2004.03.099

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Fluidized bed combustion is one of the advantageous technologies for coal and/or incineration firing especially with respect to the environmental protection of emissions, such as NOx/SOx. Bed material movement in such a fluidized bed has a prime importance in the heat transfer process. Thus, quantitative measurement of the bed material movement and the void fraction are indispensable for better understanding of the fluidized bed. In this investigation, neutron radiography is applied to visualize the bed material movement in a simulated fluidized bed heat exchanger installed with vertical tubes. Bubble behavior and void fraction profile are obtained by the image processing technique. Bubble movement is highly restrained by these vertical tubes, so that the bubbles rise up along the tube. The bubble diameter is well correlated by the modified Mori and Wen's correlation taking into account the pitch of the tube arrangement. The bubble rise velocity and void fraction are well correlated by applying the drift-flux model. © 2003 Wiley Periodicals, Inc.

DOI： 10.1002/htj.10127

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Other Link： http://hdl.handle.net/10112/4950

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE INC  

In the field of the air separation technology, the downward-flow-type system has started operation for the main reboiler-condenser instead of the natural-circulation-type system. The downward-flow-type main reboiler-condenser has an advantage in the cost and the ability compared with the natural-circulation-type. while the estimation of heat transfer characteristics has a significant influence on the system performance, In this study, heat transfer experiments have been conducted by using a downward flow of liquid nitrogen (LN2). The comparison of the heat transfer coefficients with existing correlations is discussed. Estimation methods of the flow rate and the pressure drop are also discussed including the prediction of the flow instability. (C) 2002 Elsevier Science Inc. All rights reserved.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE INC  

Heat transfer characteristics of tube-banks immersed in a fluidized bed are dominated by the time averaged as well as fluctuating characteristics of fluidized-particle movement especially in the neighboring region of heat transfer tube. Quantitative flow visualization of the fluidized bed installed vertical tube-banks has been successfully conducted using neutron radiography and image processing technique. The quantitative data of void fraction distribution as well as the fluctuation data are presented. The bubbles formed in the bed rise along by the vertical tubes and observed bubble size is smaller than that in a free bubbling bed without tube-banks. The bubble diameter is well correlated by the modified Mori and Wen's correlation. The bubble rise velocity is also well correlated by applying the drift-flux model. These results are consistent for both tested bed materials of Geldard's B- and A- particles, while the bubble size is significantly different between two kinds of particles. (C) 2002 Elsevier Science Inc. All rights reserved.

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Language：English   Publishing type：Research paper (scientific journal)  

In fluidized-bed boilers, many kinds of particles, e.g., coal, sand, refuse derived fuel (RDF) and limestone, exist. In such binary systems of particles, the segregation may occur, which harms the combustion and thus heat transfer in bed. The particle that rises up in a fluidized-bed is referred to as "flotsam", and the particle that sinks into a fluidized-bed is referred to as "jetsam". Whether a given particle in a fluidized-bed becomes the flotsam or jetsam depends on many factors, such as the density ratio, size ratio, shape of the particle, fluidization velocity, shape of the gas distributors and the material packing ratio. Owing to these complexities, the segregation phenomenon has not been fully understood. In this paper we describe movements of large particles (38 mm spherical balls) in a fluidized-bed (300 mm width 100 mm depth 700 mm height) obtained by the visualization using neutron radiography. In experiments, tracer particles were mixed into the bed, and particle image velocimetry (PIV) and particle tracking velocimetry (PTV) were used to analyze the movement of the large particles and fluidized-bed materials. Visualization results clearly indicated the interaction among large particles, bed materials and bubbles in the bed.

DOI： 10.1080/10589750108953092

Scopus

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Language：English   Publishing type：Research paper (scientific journal)  

A single-bubble movement and induced bed-material movement were fundamental processes in the flow mechanism of a fluidized-bed. A single gas bubble was injected into the fixed-bed with the tracer particles (B4C) and the flow field around the bubble was visualized using neutron radiography. The image processing technique was applied to the visualized images and the velocity field was obtained by using PIV (Particle Image Velocimetry) technique. The result clearly showed bed-material movement around the rising bubble, i.e., the transverse movement at the roof of the bubble, the free fall or downward motion at the side and the upward motion in the bubble wake.

DOI： 10.1080/10589750108953092

Scopus

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST CHEMICAL ENGINEERS  

Recent advanced technologies in boiler manufacturing bring about highly efficient and compact water-tube boilers for gas firing or oil firing. These boilers have very simple water-circulation system, which often brings about flow instabilities followed by critical heat flux, CHF, problems. This paper describes such an oscillatory flow (CHF) at relatively low mass flux and at low pressure. CHF is a decreasing function of the amplitude and period of the flow oscillation, and reaches almost 40 % of the steady state value. When the tube wall is thin, CHF is mainly controlled by the two-phase flow dynamics and is well simulated using a simple lumped-parameter model of boiling channel. At very low mass flux, CHF depends significantly on the how orientation, and is closely related to the flow pattern transition.

Web of Science

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Language：Japanese   Publisher：THE JAPANESE SOCIETY FOR MULTIPHASE FLOW  

Fluidized-bed combustion systems are composed of many kinds of particles with a variety of sizes, e.g. coal, sand, RDF, limestone etc. In such a binary system of particles, the segregation, if occurs, may harm the combustion, mixing and heat transfer in the bed, depending on the particle movement. The particle movement or circulation in the fluidized-bed depends on many factors, such as the density ratio, size ratio, shape of particle, fluidization velocity. Owing to the difficulty of flow visualization, such particle movement has not been fully understood so far. This paper describes large-particle movement obtained by the flow visualization using neutron radiography. Tracer particles mixed into the fluidized particles indicated clearly bubbles and the cloud behavior around the bubble. Image processing, i.e. PIV and PTV, gives rather clear understanding on the interaction between the large particle, emulsion and/or cloud behavior in the bed.

DOI： 10.3811/jjmf.14.451

CiNii Books

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Other Link： http://hdl.handle.net/10112/4940

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Heat transfer characteristics of tube-banks immersed in a fluidized-bed is dominated by the time-averaged as well as statistical characteristics of bed-material movement, especially, in the neighboring region of heat transfer tube. The neutron radiography and image processing technique have been successfully applied to the visualization of flow field and quantitative measurement of void fraction in the bed. This quantitative visualization technique is verified as a useful means in understanding the flow behavior and thus the heat transfer mechanisms.

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The bulk movement of fluidized bed material was visualized by neutron radiography by introducing tracers into the bed materials. The simulated fluidized bed consisted of aluminum plates, and the bed material was sand of 99.7% SiO(2) (mean diameter: 0.218 mm, density: 2555 kg/m(3)). Both materials were almost transparent to neutrons. Then the sand was colored by the contamination of the sand coated by CdSO(4). Tracer particles of about 2 mm diameter were made by the B(4)C, bonded by the vinyl resin. The tracer was about ten times as large as the particle of fluidized bed material, but the traceability was enough to observe the bed-material bulk movement owing to the large effective viscosity of the fluidized bed. The visualized images indicated that the bubbles and/or wakes were important mechanism of the behavior of the fluidized bed movement. (C) 1999 Elsevier Science B.V. All rights reserved.

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Scripta Technica Inc  

Critical heat flux (CHF) is reduced by flow oscillations. The reduction of CHF is significantly influenced by flow oscillation period and amplitude, heat capacity of test tube, and mean inlet mass flux. A scaling parameter of the temperature response of the tube wall was derived based on a lumped-parameter model of the tube wall's heat capacity. When this scaling parameter was applied to CHF under flow oscillations, the experimental data were successfully correlated.

DOI： 10.1002/(SICI)1523-1496(1999)28:6<541::AID-HTJ10>3.0.CO;2-E

Scopus

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

A simulated fluidized-bed heat exchanger with tube banks was visualized using a neutron radiography system. Observed flow pattern indicated an importance of the tube arrangement. Heat transfer experiment, conducted simultaneously, indicated a close relationship between the heat transfer and flow pattern. The staggered arrangement with relatively small pitch has a potential of high heat transfer performance.

Web of Science

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Flow visualization of the behavior of a large particle in a fluidized bed was conducted using neutron radiography. The large particle moved according to the bed materials, especially in the wake of a bubble. When the density of the large particle was high, the particle moved with a velocity different from that of bubble, and in some cases the particle moved downward through a bubble. When the density was low enough, the particle moved on the surface of the bubble wake. The drag force of the large particle immersed in the fluidized bed was measured. The drag force increased with increase in the volumetric gas flux as well as with increase in the particle diameter. The drag coefficient was derived and was well correlated on the basis of a two-phase model and experimentally determined effective viscosity of the bed materials.

DOI： 10.1299/kikaib.62.3413

CiNii Books

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Other Link： http://hdl.handle.net/10112/4702

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Flow visualization of cross-flow tube-banks in a simulated fluidized-bed was conducted by using the neutron radiography system of JRR-3M. Applying the image processing technique to the visualized image, the void fraction profile in the tube-bank was obtained. The observed flow pattern and the void fraction profile demonstrate the importance of the tube arrangement in fluidized-bed hear exchangers.

Web of Science

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE PUBL B V  

Web of Science

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Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Web of Science

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Venue：東京  

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Venue：Zoom(東京)  

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Venue：Zoom(佐賀)  

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Venue：Zhenjiang, China.  

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Venue：東京  

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Venue：東京  

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Venue：京都大学複合科学研究所  

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Venue：富山  

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Venue：富山  

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Venue：吹田  

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Venue：吹田  

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Venue：吹田  

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Venue：宇部  

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Venue：宇部  

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Venue：Nagasaki, Japan  

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Venue：Nagasaki, Japan  

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http://www.rri.kyoto-u.ac.jp/PUB/report/PR/ProgRep2017/ProgRep2017.html

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Venue：調布  

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Venue：Toyohashi JAPAN  

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Venue：伊都  

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Venue：Kobe,Japan  

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Venue：Kyoto, Japan  

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Venue：Osaka, Japan  

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Venue：Osaka, Japan  

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Venue：札幌  

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Venue：大阪  

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Venue：Grindelwald CH  

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Venue：Kyoto, Japan  

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Venue：Kyoto, Japan  

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Venue：Nagano, Japan  

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Venue：Chiba, Japan  

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Venue：大阪  

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Venue：大阪  

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Venue：Kumamoto  

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Venue：熊本  

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Venue：Kumamoto  

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Venue：Kumamoto  

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Venue：Kashiwa  

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Venue：Kashiwa  

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Venue：Incheon, Korea  

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Venue：Incheon, Korea  

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Venue：Osaka, Japan  

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Venue：Osaka, Japan  

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Venue：Delft  

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Venue：Delft  

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Venue：Hamamatsu, Japan  

There is still not enough knowledge of thermal-fluid characteristics in helically coiled tube under flow instability condition. In this investigation, experiment was conducted by using a natural circulation loop with liquid nitrogen as working fluid. The test section was helically coiled tube and had 4 mm in inner tube diameter, 100 mm in coil diameter and 3150 mm in heated length. The experimental condition was inlet throttle valve Kin = 540, 1076, 2065, and system pressure pex = 0.3, 0.5 MPa. As an experimental result, a inlet flow rate, boiling heat transfer and critical heat flux had been evaluated including post-dryout condition.

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Venue：Hamamatsu, Japan  

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Venue：Hamamatsu, Japan  

Critical Heat Flux (CHF) in a non-uniformly heated tube under inclined upward flow conditions is very important factor in designing actual boiling systems. However, only a few investigations on the CHF have been conducted under these conditions. Consequently, in the series of investigations, the experimental study on the CHF of non-uniformly heated tube was conducted with 900 mm and 1800 mm in heated length under the inclined condition. In this study, the CHF experiment was conducted with 450 mm in heated length under several inclination angles, i.e. 15, 30, 45 and 90 degree. The characteristic of CHF is decided by the relation between the gravity and the liquid film lift up, and these effects have been able to be categorized by using the modified Froude number well.

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Venue：Hamamatsu, Japan  

Dryout of counter-current two-phase flow is widely observed in the actual chemical and/or industrial systems. In case of the diabatic counter-current two-phase flow, the upward gas increases with the liquid film evaporation along the heating tube and flooding strongly affects the dryout of counter-current two-phase flow. In this investigation, the dryout experiment was conducted with the counter-current two-phase flow consisted of the free falling liquid film and upward gas flow. The obtained dryout characteristics were strongly influenced on the degree of inlet subcoooling, and are classified into three groups on the basis on the dryout mechanism.

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Venue：Hamamatsu, Japan  

To understand the heat transfer characteristics in fluidized bed, the particle convection becomes the most important factor in the bed. In this investigation, the heat transfer experiment under a forced particle convection was conducted by using the cylinder-shaped fluidized with stirrer, and we measured a temperature in the bed. In this experiment, several sizes of particles (dp=0.2mm, 0.4mm, 1.0mm) were used. As a result, there was a sharp temperature drop in the first layer from the heating surface. And the experimental results were estimated by using a simple heat transfer model with effective thermal conductivity, particle-gas heat transfer coefficient and thermal contact resistance.

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Venue：Hamamatsu, Japan  

In this research, flow pattern and pressure drop characteristics of kerosene-water two phase flow in horizontal mini-channel was investigated. The tube diameter was 0.53 mm, and it was made from pyrex glass. The volumetric fluxes of each liquids were set between 0.05 and 0.6 m/s. The several flow patterns were observed in mini-channel, i.e. Droplet flow, Slug flow, Slug-Annular flow, Annular flow, Parallel flow and Kerosene slug flow. The transition of flow pattern has been explained by using Weber number of each phase. The pressure drop has shown a good agreement with Lockhart-Martinelli correlation, moreover the adaptability of the moving film model to the estimation of pressure in the slug flow regime has been confirmed.

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Venue：大阪  

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Venue：京都  

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Venue：Tokyo, Japan  

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Venue：岡山  

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Venue：岡山  

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Venue：大阪  

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Venue：大阪  

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Venue：大阪  

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Venue：Rochester  

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